Thursday, July 11, 20244:00 PM - 5:00 PM MPP01 Presentation Time: 4:00 PM

Purpose

There have been recent disruptions in supply chains related to centering baskets intended for use with high dose rate (HDR) endobronchial brachytherapy. The standard plastic catheter (1.6mm diameter) without a centering basket gives too high of a surface dose to the bronchial mucosa to safely prescribe at distances of 5-10mm. We present on the commissioning and first reported clinical use of intraluminal endobronchial HDR brachytherapy by placing a standard plastic catheter within a robotic bronchoscope working channel, functioning as a fixed spacer of the source from the bronchial mucosa.

Materials and Methods

In this first in-human hybrid technique, a 68-year-old patient with an endobronchial tumor obstructing the lower left lobe in the superior segment of the bronchus received a definitive treatment with the HDR source. The patient previously received external beam radiation to the right upper lobe (24Gy in 1 Fractions) and 2 nodules in the left lower lobe (60Gy in 5 Fractions) of the lungs. The system was commissioned by measuring attenuation from the robotic bronchoscope (Intuitive Surgical, Inc., Sunnyvale, CA, USA) to determine scaling required for water-based TG43 dose calculations. Well chamber readings were taken with the Ir-192 HDR source inside the plastic catheter with and without the bronchoscope using a custom 3D printed well chamber insert. In preparation for clinical use, standard treatment plans were created in Eclipse (Varian Medical Systems, Inc., Palo Alto, CA, USA) in cm increments prescribing at 5mm or 10mm from the bronchoscope wall. Following general anesthesia, a therapeutic bronchoscope was inserted to perform tumor ablation and mechanical dilation in the occluded airway. After airway patency was achieved, the shape sensing robotic assisted bronchoscope was passed distal the endobronchial tumor. Tumor length was determined with the robotic bronchoscope, by marking the junction of the robotic catheter at its intersection of the endotracheal tube, both distal and proximal to the tumor. The HDR brachytherapy catheter was then inserted through the robotic catheter and placement was verified with fluoroscopic imaging and a radiopaque wire with fiducials in cm increments. Once alignment was verified, the brachytherapy catheter was secured to the robotic catheter using adhesive. The treatment plan was created with 1 cm proximal and distal margins. Catheter length was confirmed and obstruction check through the catheter was completed prior to delivery.

Results

The attenuation measurements from the bronchoscope were <1% over a length of 1 to 8 cm indicating no need to scale treatment delivery time. The bronchoscope's diameter of 3.8 mm significantly reduced the bronchial mucosal dose (by ∼2 times, ∼70 Gy vs. ∼30 Gy at tissue surface for 7.5 Gy/Fraction) compared to the standard plastic catheter without a centering basket. The patients’ tumor was 2 cm in length, and the treatment plan ensured dose (22.5 Gy in 3 Fraction) ±1 cm of the tumor (4 cm treatment length) prescribed at a depth of 0.5 cm from tissue surface. The patient was discharged home the same day in stable condition without acute complications.

Conclusions

HDR brachytherapy with a catheter within a robotic bronchoscope's channel was feasible as an alternative to the standard plastic catheter for endobronchial treatment.